Solvent and water-based crosslinkable polymers have wide utility in industry as coatings and adhesives. Current and proposed environmental regulations have been instrumental in the development of formaldehyde- and isocyanate-free coatings in an effort to reduce health hazard materials used in coatings. One relatively new type of water-borne system is based upon a polymeric system having a plurality of acetoacetate groups and a crosslinker system of blocked polyamines which is capable of reacting with the acetoacetate groups. Recently developed blocked polyamine crosslinkers for acetoacetate coatings are based upon benzaldimine chemistry. Publications describing acetoacetate chemistry as well as that associated with benzaldimine crosslinking systems are as follows:
European Patent EP 0 552 469 discloses polyacetoacetate resins curable with a crosslinker comprising a multifunctional benzaldimine. In the background of EP '469, the patentees point out that U.S. Pat. No. 3,668,183 discloses the use of a blocked aldimine or ketimine generated by the reaction of polyamine and an aliphatic ketone or aliphatic aldehyde as a curative for polyacetoacetate resins to form polyenamine resins. The patentees of '469 point out the aliphatic aldimine crosslinking system is moisture intolerant and that gloss and solvent resistance are not as high as desired. European '469 suggests the formation of a two component coating composition comprising a polymer containing a plurality of acetoacetate functional groups as a first component and a second component consisting of an aromatic aldimine having the structure: ##STR1## where R.sub.1 is an aryl group, R.sub.2 is a hydrocarbon, a polyalkylether, an oligomeric adduct or an acrylic polymer which may contain at least one group, such as a secondary amine which will react with the acetoacetate groups, and n is greater than 2 unless another acetoacetate reactive group is present. Both solvent and water-borne coatings are prepared.
An article by Kim, et al., Utilization of the Novel Acetoacetate Chemistry and Solvent and Water Borne Coatings, presented at the Water Borne, Higher-Solids and Powder Coating Symposium, Feb. 24-26, 1993, supplements European '469 EPO. Two component coating systems based upon acetoacetate functional polymers employing an aromatic aldimine as the crosslinker are described. Again, at least two aldimine groups or an aldimine and at least one other acetoacetate reactive group are present in the crosslinker.
U.S. Pat. No. 5,288,804 is the U.S. companion to European '469 and to the article by Kim, et al.. It too, pertains to curable polyacetoacetate resins having low solvent loading using a multifunctional benzaldimine as the curing agent.
U.S. Pat. No. 4,743,668 discloses vinyl polymers containing polymerized N-acetoacetylacrylamide units which are found useful for effecting coagulation, flocculation and dewatering of wet slurries. One of the monomer structures is represented by the formula: ##STR2## wherein R is H or CH.sub.3. This monomer then is polymerized with a variety of other ethylenically unsaturated monomers, e.g., vinyl acetate, acrylic acid, acrylamide, vinylethers, maleic anhydride and so forth. Other monomers include acrylonitrile, various acrylic and methacrylic acid esters and the like. These polymers then are contacted with a bisulfite salt to form a sulfonate substituted material.
U.S. Pat. No. 4,908,403 discloses the production of pressure sensitive adhesives from acetoacetoxy-alkylacrylate polymers by emulsion polymerization. The monomers are generally defined by the formula: ##STR3## wherein R.sub.1 is a divalent organic radical and X is an organoacyl or cyano group. The monomer is polymerized with other ethylenically unsaturated monomers, e.g., vinyl esters of carboxylic acids which include vinyl acetate and vinyl propionate; alpha-beta-unsaturated hydrocarbons, such as ethylene and propylene, and other monomers, e.g., vinyl chloride and alkyl esters of acrylic and methacrylic acid, as well as acrylic and methacrylic acid. The resultant polymers have acceptable adhesive strength without crosslinkers such as N-methylolamides.
In one effort (U.S. Pat. No. 5,214,086), a crosslinking system containing a hydroxyl functional resin, at least one isocyanate functional resin and a di- or multi-aldimine or ketimine functional moiety was described. The crosslinking occurred at either ambient temperature or a higher temperature, the aldimine being used to accelerate the cure rate of the hydroxyl-containing polymer with the polyisocyanate.
U.S. Pat. No. 5,332,785 discloses liquid coating compositions comprising acetoacetate modified epoxy resins and blocked polyamines, e.g., aldimines. Hydroxyl-containing polyepoxides are converted to acetoacetate-modified resins through transesterification using alkylesters of acetoacetic acid.